1. Field of the Invention
The present invention relates to a laminar structure of semiconductor, in particular to a laminar structure of semiconductor that is applied to a semiconductor component.
2. Description of the Prior Art
Among semiconductor materials, gallium nitride (GaN) is provided with good electrical conductivity, thermal conductivity and thermal stability, and thus can be used as high-power components. In addition, due to the wide band-gap, GaN is capable of emitting at the green to violet wavelength and is also suitable as a full-color light-emitting element. However, the substrate, such as silicon substrate, for epitaxial growth of GaN has huge differences in lattice constant and thermal expansion coefficient from GaN, namely 17% and 46%, respectively; therefore, there exists considerable stress field between these two. Bending or crack due to excessive tensile stress may occur during the cooling process after completion of GaN epitaxial film growth and result in reduced component yield. Adopting a sapphire (Al2O3) substrate may have the same problem (16% lattice mismatch and 34% differences in thermal expansion coefficient) with higher cost. In addition, silicon carbide (SiC) can also be used as the substrate (3.5% lattice mismatch, and 25% differences in thermal expansion coefficient). However, the cost of SiC is too high for commercial development.
Furthermore, a buffer layer may be arranged between the substrate and the epitaxial layer to reduce the lattice mismatch and further stress. However, the buffer layer must be provided with good lattice structure in order to grow the epitaxial layer with good quality; therefore, it still needs high-temperature crystal growth process, which is complicated and expensive.
Regarding a laminar structure of semiconductor for reducing the stress, referring to FIG. 6, CN Patent Publication No. CN101901752A disclosed a laminated semiconductor structure 1, substrate 2, a first film 3, a buffer layer 4, the second film 5, wherein the thermal expansion coefficient of the first film is lower than that of the substrate 2, and the thermal expansion coefficient of the second film 5 is higher than that of the substrate, so that the substrate 2 and all the films (3,4,5) remain hardly warped state at room temperature.
TW Patent Publication No. TW201133938 discloses a semiconductor light emitting device with curvature control layer made of a polycrystalline α-Al2O3 and deposited on the substrate by electron beam ion or sputtering deposition. The curvature control layer has a greater thermal expansion coefficient than GaN epitaxial layer. CN Patent Publication No. CN102479683 disclose a GaN layer and a silicon nitride material (high CTE layer) and the thermal expansion coefficients of the GaN layer and the silicon nitride material is greater than that of the silicon substrate so as to solve wafer bending/deformation/defect caused by differences in coefficient of expansion and achieve flat effect for wafer. However, better compatibility between the epitaxial layer and the substrate is still a goal to be achieved.
It is now a goal to develop a laminar structure of semiconductor, which can reduce the effect of stress between the epitaxial layer and the substrate to avoid bending or crack caused by stress to further achieve enhanced yield. In addition, if the manufacturing process may be simplified, the cost may be saved and the application fields may be broadened.